The present invention relates to laser transmitters of the type that are useful for surveying or for spatial positioning at a construction site or elsewhere. Such laser transmitters project a thin beam of laser light or a fan-shaped beam of laser light, and rotate the beam about a rotation axis, have been in use for a number of years at construction sites. Such transmitters can be used with manual surveying systems and also as a part of automated surveying systems. Laser transmitters of this type can also be used in spatial positioning systems that provide for control of earthmoving machines, and the like, to shape a construction site to a desired contour.
Laser transmitters of this type typically have self-leveling and automatic orienting capabilities. The laser transmitter is typically positioned at a worksite on a support tripod and then roughly leveled manually. A worker will manually adjust the transmitter housing while watching bubble vials. Fine leveling is then effected automatically by adjusting the orientation of the laser and associated optics inside the transmitter housing. Additionally, if it is desired to project a slightly tilted beam, the orientation of the laser and associated optics will be tilted inside the transmitter housing. In either event, the housing remains stationary and electric motors drive a gimbal mounting arrangement that supports the laser and associated optics to achieve the desired level or tilted orientation automatically. A control arrangement uses electrical level vials that move with the gimbal mounting arrangement, and that provide an electrical indication when the gimbal mounting arrangement has been moved to the desired orientation.
A difficulty encountered with such an arrangement is that the level motors could conceivably cause the gimbal arrangement to tilt by too much with respect to the housing, with the result that the laser or other movable internal components could be driven into contact with some portion of the housing or with other parts of the transmitter. Such contact could cause damage to the laser or other parts of the transmitter. In the past, to prevent this damage, a series of mechanical limit switches have been used that are actuated when the laser and associated structures reach the end of their normal range of travel in either direction along either of two orthogonal axes. Such mechanical limit switches are difficult to configure and calibrate, however. Further, mechanical limit switches are closed when the end of travel is reached, but provide no indication as the end of travel is about to be reached. Therefore, the movement of the transmitter internal gimbal supports must necessarily be undesirably slow.
Other problems result from using mechanical limit switches to detect the end of travel of the gimbal support arrangement. Because mechanical limit switches must necessarily be relatively close to bosses or other structures on the interior of the transmitter housing so that the switches can be actuated by contact with the bosses or other structures, a transmitter using such switches is not as rugged as might be desired. If the transmitter is inadvertently dropped and one of the switches is relatively close to the interior of the housing, the switch can strike the interior of the housing, resulting in damage.
Further, it will be appreciated that if, for example, four switches used in a transmitter to detect the end of travel in either direction along either of two orthogonal axes, it is possible that the gimbal support arrangement may be moved so that the maximum tilt of the laser and components with respect to the housing actually occurs along an axis that is between the axes on which the mechanical switches is situated. To take this into account, the mechanical limit switches must be arranged to be actuated when the gimbal support arrangement is tilted by a lesser amount along an axis on which the switches are positioned. As a consequence, the interior of the housing must be designed in a way that is less than optimum to assure that the gimbal support arrangement and other movable components do not come into contact with the housing.